Existing 3GPP systems, including 2G/3G systems and the newly emerging SAE/LTE system, support the possibility to trace a particular user throughout its lifetime in the network. Typical use of trace is to troubleshoot problematic user connections such as in response to user complaints. Another use is to monitor generic network performance and to perform root cause analysis to identify network problems.
The user may be traced based on the user identity (IMSI based trace), the terminal type (IMEI based trace) or based on location (cell trace). During tracing all network activities related to the particular user can be logged and later delivered to a network management entity for evaluation. Logged network activities include signaling messages sent and/or received either on the radio interface and/or on the network node interfaces. Details of the trace functionality may be found in documents “3GPP TS 32.421 Subscriber and equipment trace: Trace concepts and requirements,” “3GPP TS 32.422 Subscriber and equipment trace: Trace control and configuration management,” and “3GPP TS 32.423 Subscriber and equipment trace: Trace data definition and management.”
The trace target and the trace configuration are specified by a management entity such as an OAM (Operation & Maintenance) entity, which sends the configuration to the involved network nodes. In the trace configuration there is possibility to specify the interface(s) from which the trace logs are to be collected as well. Also, the level of trace information details may be specified. For example, all message elements may be logged or only the most relevant ones may be logged.
In current 3GPP systems there are two ways to activate tracing, either via “signaling based activation” or “management based activation”. In the signaling based activation, the trigger for tracing a particular user is propagated piggy-backed on the regular signaling messages sent between the network nodes which the given user flow passes through. Initially the management system configures the particular user for tracing in the HSS (Home Subscriber System) based on its IMSI (International Mobile Subscriber Identity). As soon as the user with the given IMSI appears in the system and the HSS is interrogated for user information such as security credentials at user attach, the trace trigger will be propagated to related network nodes via the invoked signaling flow.
In the management based activation, the trace trigger is not propagated to other nodes. Instead, the management system configures selected network nodes to trace a particular user or set of users. When a new user appears at the given network node, it evaluates the selection criteria and starts trace recording in case the criteria is satisfied.
A more recently studied use case of trace in 3GPP is the MDT (Minimization of Drive Test) measurements performed by the UE (user equipment). The MDT measurements are collected within the framework of the trace concept, where the UE is a trace entity itself that needs to be triggered for tracing just like any other network entity.
One problem with existing trace method is that there can be situations when the trace trigger reaches the involved network node such as the eNB (in case of LTE) or the UE (in case of the MDT measurements) only after the first UE messages have passed through the node or after the first messages has been sent from the UE. Thereby the initial messages of a UE connection cannot be registered, which means that the trace log will be incomplete and any network analysis or root cause analysis done later based on this information will be inaccurate and problematic. Due to the incompleteness of trace logs certain network problems may remain undiscovered by the management system.